ABSTRACT Average survival times for glioblastoma patients remain around 15 months because of relatively few effective treatments. CD11b+ Tumor-associated myeloid cells, can account for up to 40% of the tumor mass, are well known to suppress anti-tumor immunity, and directly promote tumor growth. While significant advances have been made in the development of TAMC-targeted therapies, analysis of TAMCs requires analysis of surgically resected tumor tissue. In this R21 application we propose that development of a novel tracer, Cu-64 labeled antibody fragments, which will allow for non-invasive PET imaging of TAMCs in glioblastomas. We will therefore, test our novel hypothesis that Cu-64-labeled monobodies or diabodies derived from the m1/70 hybridoma will enable quantification TAMC infiltration into the tumor and monitoring of TAMC-targeted immunotherapies. We will first generate and test the sensitivity of our antibody fragments following injections of varying concentrations of CD11b+ mouse spleenocytes from C57BL/6j mice into CD11b-knockout C57BL/6j- background syngeneic glioma-bearing mice (Aim 1). We will then demonstrate that our novel antibody fragments can be used to monitor TAMC-targeted therapies including anti-Gr1-antibody, Celecoxib, or a CSF-1R inhibitor in the GL261 syngeneic glioma model, and a de novo glioma model (AIM 2). As the m1/70 clone can recognize both human and mouse CD11b, we believe that our preclinical studies can lead to quick translation of our findings into TAMC-targeted clinical trials in patients with glioblastoma, or in patients with other neuroinflammatory disorders. !